High-speed manufacturing of printed product micro features

ABSTRACT

A method for manufacturing a printed product comprises provision of a matrix comprising a matrix surface having at least one recess. A first curable compound is applied to the matrix surface in a controlled amount that does not exceed a volume of the recess(es). The first curable compound creep down in and partly fill the recess(es), leaving protruding surfaces substantially free from the first curable compound. The matrix surface and recess(es) are covered by a pickup layer of a second curable compound. The matrix is brought in contact with the substrate surface and the first curable compound and the second curable compound are cured. The matrix surface is separated from the substrate surface, leaving the pickup layer and the first curable compound on the substrate surface. The first curable compound forms printed product micro features at the pickup layer covering the substrate surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of copending U.S. application Ser. No.14/440,303, filed on May 1, 2015, which was filed as PCT InternationalApplication No. PCT/SE2013/051253 on Oct. 25, 2013, which claims thebenefit under 35 U.S.C. § 119(a) to Patent Application No. 1251247-1,filed in Sweden on Nov. 2, 2012, all of which are hereby expresslyincorporated by reference into the present application.

TECHNICAL FIELD

The present invention relates in general to manufacturing of printedproducts, and in particular to a manufacturing method and an arrangementfor producing printed products having printed product micro featuresarranged on a surface of a substrate sheet.

BACKGROUND

Optical arrangements giving rise to a synthetic three-dimensional imageor an image that changes its appearance at different angles have beenused in many applications. Besides purely esthetical uses, sucharrangements have been used e.g. as security labels on bank-notes orother valuable documents, identification documents etc. or as brandprotection. The synthetic three-dimensional images have also been usedfor providing better geometrical understanding of complex shapes in e.g.two-dimensional information documents.

Synthetic image devices are based on the interaction between an array offocusing elements and micro image portions. In some prior art “syntheticimages” are also referred to as “integral images” or “moiré images”,since the experienced image is composed of a number of parts interpretedtogether as an integral unit. The relative geometrical relation givesrise to different optical effects, from different levels of 3D to imagesthat move or change its appearance e.g. dependent on the viewing angle.The focusing elements and the micro image portions are typicallyprovided by printing on an essentially transparent polymer film.

One approach for manufacturing a synthetic image device is disclosed inthe published International patent application WO 2011/102800 A1. Here aroll-to-roll process is achieved by the interaction of a matrix rollwith a substrate. The matrix roll comprises recesses that are filledwith a curable compound. The curable compound is transferred onto thesubstrate during a rolling contact between the matrix roll and thesubstrate. Typically, in order to facilitate the adhesion of the curablecompound to the substrate, the surface of the substrate is pre-treated,e.g. provided with a surface layer. A good adherence between thatsurface layer and the curable compound in the matrix roll assists inremoving the curable compound from the recesses when the rolling contactends.

An image object in many applications of an optical arrangement thatprovides a synthetic integral can be coloured to obtain a black andwhite image, a greyscale image or a coloured image, or simply to provideproper optical properties. This colouring may typically be obtained byfilling the recesses in the matrix roll with ink. This operation is achallenge, in particular in large-scale production using for example theabove mentioned roll-to-roll arrangement, since the embossed cavities,ranging from μm-sized cavities to cm-sized cavities, should all beequally filled without leaving residual ink on intermediate surfaces.

When the ink is transferred to the substrate sheet, the ink may bespread outside the area defined by the recesses. This is particularlycumbersome if the substrate is provided with a surface layer forimproving the adhesion properties. The contact between the substrate andthe matrix roll is typically quite intense, at least at a micro level,and the contact force causes the surface layer to shear between thesubstrate and the matrix roll. This increases the risk for dragging inkout along from the recesses.

One way to mitigate such effects is to pre-cure the ink before it comesinto contact with the surface layer of the substrate. The larger theprinting speed is, the higher level of pre-curing is needed tocounteract any shearing action of the surface layer. However, pre-curingof the ink within the recesses makes it in general more difficult torelease the ink from the recesses and the risk that the ink becomesstuck in the matrix recesses thereby increases. These releasing problemsalso typically increase with increasing printing speed. If the ink iscured too much before the contact with the surface layer is established,any cross-linking between the surface layer and the ink will also bereduced, reducing the adhering effect of the surface layer.

Another problem is removal step for excess ink. First, the removalwiping causes wear, which shortens the life of the printing matrices.Secondly, in order to achieve a thorough wiping, the printing speed hastypically to be limited. A too high printing speed will typicallydeteriorate the wiping efficiency and thereby the quality of the finalproduct.

In other words, in prior art manufacturing approaches there might beink-spreading problems and wear problems when they are used inhigh-speed manufacturing.

SUMMARY

One object of the invention is to facilitate high-speed printing of highaccuracy product micro features on a surface of a substrate sheet. Theabove object is achieved by a method for manufacturing, an arrangementand results in a synthetic image device according to the enclosedindependent claims. Preferred embodiments are defined by the dependentclaims. In general words, in a first aspect, a method for manufacturinga printed product comprises providing of a matrix comprising a matrixsurface having at least one recess. A first curable compound is appliedto the matrix surface and the recess(es) in a controlled amount thatdoes not exceed a volume of said recess(es). The first curable compoundcreep down in and partly fill the recesses, leaving protruding surfacessubstantially free from the first curable compound. The matrix surfaceand the at least one recess partially filled with the first curablecompound is covered by a pickup layer of a second curable compound. Thematrix is brought in contact with the substrate surface and the firstcurable compound and the second curable compound are cured, at leastpartly. The matrix surface is separated from the substrate surface,leaving the first curable compound on the substrate surface. The pickuplayer and the first curable compound filling the at least one recess arethereby transferred together from the matrix surface onto a substratesurface of a substrate sheet. The first curable compound thus formsprinted product micro features at the pickup layer covering thesubstrate surface.

In a second aspect, an arrangement for continuous production of aprinted product comprises a matrix roll, a first applicator, a secondapplicator, a drive unit, substrate guides and curing means. The matrixroll has a circumferential surface with at least one recess. The firstapplicator is arranged for application of a first curable compound ontothe matrix roll in a controlled amount that does not exceed a volume ofthe recess(es). The first curable compound creep down in and partly fillthe recess(es), leaving protruding surfaces substantially free from thefirst curable compound. The second applicator, separate from the firstapplicator, is arranged for covering the circumferential surface and theat least one recess filled with the first curable compound by a pickuplayer of a second curable compound. The drive unit is arranged forrotating the matrix roll in a rotational direction. The substrate guidesare arranged for bringing a substrate sheet in contact with the matrixroll in a contact section. The contact section is situated, in therotational direction, after the second applicator. The first curablecompound forms printed product micro features at the pickup layercovering the substrate surface. The curing means are arranged for curingthe first curable compound and the second curable compound. The curingmeans is arranged to perform the curing at least to a part in thecontact section.

In a third aspect, a synthetic image device comprises a transparentsubstrate sheet, an array of focusing elements and, array of imageobjects and a pickup layer. The array of focusing elements is arrangedat a first side of the transparent substrate sheet. The array of imageobjects is associated with the focusing elements and arranged at asecond side of the transparent substrate sheet, opposite to the firstside. The pickup layer is provided between the array of image objectsand the transparent substrate sheet. The image objects are printedproduct micro features formed by bringing a matrix in contact with asurface of the transparent substrate sheet, where the matrix has atleast one recess partly filled with a first curable compound andprotruding surfaces substantially free from the first curable compound,and curing the first curable compound.

One advantage with the above presented technology is that it enableshigh-speed printing with reduced risk for spreading ink out from therecesses. Printing speed of above 90 m/min has been used with a samehigh quality as for lower printing speed. Other general advantages andadvantages of preferred embodiments are further discussed in connectionwith the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with further objects and advantages thereof, maybest be understood by making reference to the following descriptiontaken together with the accompanying drawings, in which:

FIG. 1 is a schematic illustration of a printed product;

FIGS. 2A-D are schematic drawings of printing situations of anembodiment of a printing method;

FIG. 3 is a flow diagram of steps of an embodiment of a printing method;

FIG. 4 is a schematic drawing of an embodiment of a printingarrangement;

FIG. 5 is a schematic drawing of an embodiment of another printingarrangement; and

FIG. 6 schematically illustrates supporting structures in largerecesses.

DETAILED DESCRIPTION

Throughout the drawings, the same reference numbers are used for similaror corresponding elements.

A product manufactured according to the present teachings comprises abody that in the product, or in an intermediate product, constitutes asubstrate sheet with a limited thickness in relation to the extension inorthogonal directions thereof. The product has printed product microfeatures arranged on, or in, one or both principal surfaces of thesubstrate sheet. By way of example, one embodiment of said product maycomprise primary product micro features on a first side of a substratesheet and secondary product micro features on the opposed side of thesubstrate sheet. The primary product micro features are typicallylocationally associated with the secondary product micro features. Otherembodiments of said product may comprise three or more sets of productmicro features. In its most basic form the product comprises a substratesheet with product micro features printed on only one surface thereof.

The product micro features can be used for different purposes, forexample as structural and/or functional elements in a synthetic imagedevice, as described above, or in other devices such as optical devices,electronic devices, micro fluidic devices, display devices,electrochemical devices, electrochromic devices, bioassay devices, etcor simply as printed ink in printed matter. In most of theseapplications the product micro features often have to be provided withhigh resolution and high dimensional tolerances since the functionalityof the product is coupled to the dimensions and/or distribution of theproduct micro features. Often the product micro features also have to besmall to obtain the desired effect.

For illustrative purposes FIG. 1 shows a product 1 manufactured inaccordance with one embodiment of the present teaching comprising anarray of micro lenses 2 and an associated array of image objects 4respectively arranged on opposite sides of a transparent substrate sheet5. The aspects of the present disclosure are mainly described in termsof manufacturing of such a product arrangement. However, the presentteachings are not limited to only this type of product but areapplicable to various kinds of products having printed product microfeatures. In such a particular embodiment, the image objects 4 areprinted on one or more pickup layers 6 (one such layer is shown,indicated by a first dotted line) arranged on the substrate sheet 5,without pre-structuring the substrate sheet 5. The micro lenses 2 mayhave been formed by embossing in the substrate sheet or by a cast cureprocess in a separate layer 7 (indicated by a second dotted line) on thesubstrate sheet 5. Although embodiments of the invention are exemplifiedwith micro lenses it should be appreciated that other elements capableof focusing at a section of, and/or restricting the view of, anassociated image object can be used to obtain an integralrepresentation. Examples of other such focusing elements, besides microlenses, are micro mirrors, apertures, lenticular mirrors and lenticularlenses. The image objects 4 are thus in this present embodiment to beconsidered as printed product micro features 3 at a pickup layer 6covering the substrate surface 10. In most embodiment described below,spherical micro lenses are used as demonstration examples.

Also the micro lenses 2 can be manufactured in a similar manner, and insuch a view, the micro lenses 2 are to be considered as printed productmicro features 3 at a pickup layer covering the substrate surface 10.

In the present disclosure, the term “matrix” is used to denote a bodyhaving a surface presenting a pattern of recesses or holes. The surfacebetween these recesses is essentially flat or is following a smoothgeneral shape, e.g. a cylinder shape. The term “matrix roll” isanalogously interpreted as a roll having an outer or circumferentialsurface exhibiting a pattern of recesses or holes. The surface betweenthese recesses follows a smooth general cylinder shape. The pattern ofrecesses corresponds to the structures that are intended to be printedonto a substrate.

In FIGS. 2A-D, some of the basic ideas of the present disclosure areillustrated schematically. I FIG. 2A, a first applicator 15 is arrangedto interact with a matrix roll 20. The matrix roll 20 has acircumferential surface 24 with recesses 22. The first applicator 20 isarranged for application of a first curable compound 12 onto the matrixroll 20 so as to fill the recesses 22 with the first curable compound12. Excess volumes of first curable compound 12 may in some embodimentsappear e.g. on the circumferential surface, but may easily be removed,as discussed more in detail further below. The first curable compound 12is provided from a first source 16 onto an application roll 14 of thefirst applicator 15. The matrix roll 20 rotates in a rotationaldirection 26 and the application roll 14 is arranged in rolling contactwith the circumferential surface 24 of the matrix roll 20 and rotatestherefore in an opposite direction. The interaction between the firstapplicator 15 and the matrix roll 20 results in a transfer of the firstcurable compound 12 into the recesses 22. In other words, the recessesare filled with fillings 28 of the first curable compound 12 whenleaving the first applicator 15. In alternative embodiments, the firstapplicator 15 can be composed of other parts, e.g. different kinds ofspray arrangements, pouring conducts, scraping edges, slot dies etc.

The first curable compound 12 is depending on the actual applicationpigmented or not. Such pigmented curable compound is often referred toas “ink”.

In FIG. 2B a subsequent part, with reference to the rotational direction26, of the matrix roll 20 is illustrated. A second applicator 30 isarranged to interact with the matrix roll 20. The second applicator 30comprises in this particular embodiment an application roll 34 and asecond source 36 for a second curable compound 32. The application roll34 is in analogy with the application roll 14 (FIG. 2A) arranged inrolling contact with the circumferential surface 24 of the matrix roll20 and rotates therefore also in an opposite direction. The interactionbetween the second applicator 30 and the matrix roll 20 results in atransfer of a layer, in the present disclosure denoted a pickup layer 6,of the second curable compound 32 onto the circumferential surface 24 ofthe matrix roll 20 and covering the fillings 28. In other words, thecircumferential surface 24 of the matrix roll 20 and the fillings 28 arecovered with a pickup layer 6 when leaving the second applicator 30. Inalternative embodiments, the second applicator 30 can be composed ofother parts, e.g. different kinds of spray arrangements, pouringconducts, scraping edges, slot dies etc.

The interaction between the matrix roll 20 and the second applicator 30is quite gentle, in order to leave a continuous pickup layer 6. This hasthe advantage that the shearing effects between the second curablecompound 32 provided by the second applicator 30 and the first curablecompound 12 of the fillings 28 becomes small. The risk for spreading thefillings 28 outside the recesses 22 is thereby very low.

In FIG. 2C, a further subsequent part, with reference to the rotationaldirection 26, of the matrix roll 20 is illustrated. Here, a substrate 5is brought into contact with the matrix roll 20, or rather the pickuplayer 6 covering the circumferential surface 24 of the matrix roll 20.The substrate is fed in a feeding direction 8 at a speed substantiallycorresponding to the rotational speed of the circumferential surface 24of the matrix roll 20. A substrate surface 10 comes into interactionwith the pickup layer 6. This process is, at contrary to the applicationby the second applicator 30 (FIG. 2B), rather intense, at least at amicro level, and high shearing forces are present. A front 39 ofmaterial from the pickup layer 6 builds up in front of the intendedcontacting point. However, these violent forces are concentrated in theouter part 37 of the pickup layer. The material of the pickup layerclose to the fillings 28 is basically more or less uninfluenced. Therisk for spreading the fillings 28 outside the recesses 22 is therebystill very low. The pickup layer 6 thereby acts as a shear forceprotection for the first curable compound 12 in the fillings 28. At thesame time, the pickup layer 6 reduces the needs for pre-treating thesubstrate surface 10. In a contact section 35 between the matrix roll 20and the substrate 5, a pickup layer 6 provided between the fillings 28and the substrate 5 is created.

Since the interaction zone between the matrix roll 20 and the substrate5 is distanced from the interface between the pickup layer 6 and thefillings 28, the integrity of the fillings 28 becomes relativelyinsensitive to e.g. printing speed. Furthermore, the need for pre-curingthe fillings 28 is reduced, which also facilitates a subsequent removalof the fillings 28 from the recesses 22.

The time aspect is also of importance in some embodiments. For certaincombinations of first and second curable compounds, the adhesion betweenthe fillings 28 and the pickup layer 6 improves with time. The timeduring which the fillings 28 and the pickup layer 6 are rotated togetherbefore entering into the contact section 35 thereby typically improvesthe adhesion. However, at too long contact periods before curing or atcertain combination of materials, there might be a risk for that thecurable compounds may dissolve more deeply into each other.

In FIG. 2D, a further subsequent part, with reference to the rotationaldirection 26, of the matrix roll 20 is illustrated. The fillings 28 andthe pickup layer 6 are cured, at least partly, in the contact section35, creating a solid-like integral coating on the substrate surface 10.At these conditions, the substrate 5 is separated from the matrix roll20, i.e. the contact section 35 ends. By adapting e.g. the viscosity,adhesion properties, curing etc. of the first and second curablecompounds 12, 32, the pickup layer 6 and the fillings 28 will follow thesubstrate 5, leaving unfilled recesses in the matrix roll 20. The firstcurable compound 12 previous constituting the fillings 28 thus formsprinted product micro features 3 at the pickup layer 6 covering thesubstrate surface 10.

Since the interaction zone between the matrix roll 20 and the substrate5 is distanced from the interface between the pickup layer 6 and thefillings 28, the integrity of the fillings 28 becomes relativelyinsensitive to e.g. printing speed. Furthermore, the need for pre-curingthe fillings 28 is reduced, which also facilitates a subsequent removalof the fillings 28 from the recesses 22.

Note that the FIGS. 2A-D are intended to show the principles in a veryschematic manner and there may in different real embodiments be variousadditional steps, devices or alternative designs.

FIG. 3 illustrates a flow diagram of steps of an embodiment of amanufacturing method. The method for manufacturing a printed productstarts in step 200. In step 210, a matrix comprising a matrix surfacehaving a plurality of recesses is provided. A first curable compound isin step 212 applied to the matrix surface and the recesses so as to fillthe recesses with the first curable compound. In step 220, the matrixsurface and the recesses filled with the first curable compound arecovered by a pickup layer of a second curable compound. The matrix is instep 230 brought in contact with the substrate surface, and in step 232,said first curable compound and said second curable compound are cured,at least partly. In step 234 the matrix surface is subsequentlyseparated from the substrate surface, leaving the pickup layer and thefirst curable compound on the substrate surface. The pickup layer andthe first curable compound filling the recesses are thus transferredtogether, indicated as a common step 240, from the matrix surface onto asubstrate surface of a substrate sheet. The first curable compound thusforms printed product micro features at the pickup layer covering thesubstrate surface. The process ends in step 299.

Selection of curable compounds is typically dependent on a lot offactors, both manufacturing related factors and requested final productproperties. In one embodiment, the first curable compound is the same asthe second curable compound. In another embodiment, the first curablecompound is different from the second curable compound. In oneembodiment, the second curable compound forms the same material as inthe substrate when being cured.

The printing process is improved by the provision of the pickup layerprior to printing. During transfer of the first curable compound theadhesion between the first curable compound and the pickup layer has toovercome the forces holding the curable compound in the recesses. Theadhesion between the curable compound and the substrate sheet 5 duringthe transferring is improved by the deposition of the pickup layer. Thepickup layer functions as an adhesive layer in the step of transferring.The pickup layer is of increased importance when pre-curing of the firstcurable compound before transferring is used since this typicallyreduces the inherent adhesive properties of the curable compound, or atleast the wetting properties of the curable compound. These adhesive, orwetting properties, are improved by applying the appropriate pickuplayer before printing.

When printing with recesses filled with a curable compound without anypickup layer, as in prior art, there is always a risk to encapsulate airpockets. Typically, such air pockets often appear close to the edge of arecess, in particular if the filling of the recess is not absolutelyperfect. When the curable compound is cured, the oxygen in the airpocket will typically prohibit or at least slow down the curing process,which then results in an air pocket with sticky, non-cured surfaces.Such unsatisfactory curing reduces the adhesion to the substrate and mayresult in that the curable compound or part thereof remains in therecess after the separation from the substrate.

By application of the pickup layer, any remaining geometries deviatingfrom the main matrix surface, e.g. not completely filled recesses, areeventually filled up. Since the pickup layer is allowed to spread alsoover the surfaces between the recesses, the complete filling of anypossible unfilled portions of the recesses is easy to achieve.

By then performing the actual printing process between two essentiallyflat and continuous layers, the risk for encapsulating air pockets issignificantly reduced. If any air pockets anyway are provided, these airpockets do at least not influence the release of the curable compoundfrom the recesses.

The first curable compound is preferably at least partly cured at somestage of the processing of the product, e.g. before the contacting withthe substrates. The first curable compound can be of a wide range ofmaterials and hence curing may be accomplished by different mechanisms.Normally the term curing is associated with polymerisation of polymermaterials initiated by irradiation, such as irradiation with ultraviolet(UV) light, and/or heating. Infrared irradiation, electron beamirradiation and the addition of chemical additives are other examples ofmeans for curing. The first curable compound may comprise non-curableconstituents as well. For the purpose of this application the termcuring also includes drying. As in many conventional printing techniquesdifferent kind of inks may be used for the curable compound. Preferablyinks with dyes are used. Pigments may cause problems when printing smallproduct micro features since the size of pigments particles usually istoo large, which may adversely affect the resolution and colour densityof the printed product micro features.

In many applications, however, not all, there is a risk for that theamount of applied curable compound is larger than the volume of therecesses. Excessive curable compounds may therefore be present above therecesses as well as on the portions of the matrix separating therecesses. One way to at least partially solve that problem is to controlthe amount of curable compound that is provided to the surface of thematrix. A pattern of recesses with a small open area basically need lessvolume of the curable compound to be filled than a pattern of recesseswith a large open area. Examples of such arrangements are discussedfurther below.

In order to avoid printing of the first curable compound on intermediatesurfaces, i.e. between and outside the printed product micro features,on the substrate sheet any excess of the first curable compound in areasof the matrix surface of the matrix outside the recesses is removed suchthat the first curable compound of the product micro features eventuallytransferred to the substrate sheet substantially originates from therecesses. By way of example, a squeegee, a clean rubber roll or the likecan be used to wipe off any excessive curable compound from the matrixsurface. Excessive first curable compound can also be removed bypolishing. Different means for removal of excessive first curablecompound can also be combined. In other words, under such conditions, itis preferable to introduce a process step, in which excessive firstcurable compound is removed from matrix surface outside the recessesbefore the covering by a pickup layer.

Ideally the first curable compound initially has a low viscosity inorder to enable the filling of small recesses of the matrix. This lowviscosity is in a preferred embodiment typically between 100 and 600mPas. However, if removing of excessive first curable compound isnecessary, using e.g. a squeegee or a polishing means, the first curablecompound may be removed from the recesses, in particular recesses havinga comparatively large open surface as compared to the depth thereof, dueto capillary forces acting on the low-viscosity curable compound. Thus ahigher viscosity of the first curable compound is desired while removingexcessive first curable compound. These contradictory requirementsregarding the viscosity of the curable compound may be overcome whenhaving equally sized recesses since the viscosity can be adapted for thesize of the recesses, but the problem is augmented when using recesseshaving sizes varying over a wide range, and in particular when thematrix comprises recesses having a large open surface, i.e. a largewidth or diameter and a comparatively shallow depth. Therefore apreferred embodiment of the manufacturing method comprises the step ofincreasing the viscosity of the first curable compound, e.g. bypre-curing, after filling of the recesses, i.e. the viscosity is lowerduring filling than e.g. during removal of excess first curablecompound. If removal of excess first curable compound is performed,preferably the viscosity of the first curable compound is increasedbefore a final removal such that the first curable compound behaves likea paste that is not significantly affected by capillary forces. Anincrease in the viscosity of the first curable compound applied to thematrix can be obtained by at least partly curing the first curablecompound. The viscosity can also be controlled by other means such as byreducing the temperature of the first curable compound.

Even if the application of the pickup layer is gentle compared to thelater actual printing process, there has to be some kind of minormechanical interaction during the application of the pickup layer. It istherefore for analogue reasons also of benefit for the application ofthe pickup layer to have a first curable compound in the recesses thathas a somewhat higher viscosity than when the first curable compound wasapplied to the recesses. In one preferred embodiment, a manufacturingprocess thus comprises the further step of pre-curing the first curablecompound in the recesses before the covering of the matrix surface andthe recesses filled with the first curable compound by a pickup layer isperformed.

However, a partially uncured first curable compound will typically havea higher adhesion to the pickup layer. Therefore, in most cases a fullycured first curable compound is not requested. In other words, in oneembodiment, by leaving the curable compound partly uncured, the adhesionto the pickup layer will be improved in some cases.

The duration of the contact between the first curable compound and thepickup layer is also important. When performing the application of thepickup layer, the wet pickup layer will to some extent start todisintegrate or dissolve the surface of the partially cured firstcurable compound in the recesses. This dissolution contributes to ahigher final adhesion between the first curable compound in the recessesand the pickup layer. When the first curable compound in the recessesand the pickup layer subsequently are cured, such disintegration isagain revoked, instead creating a strong bond between the two materials.A long contact time between the first curable compound in the recessesand the pickup layer before the common curing will increase the adhesionproperties between the materials in the final product. Such a contacttime involves at least the application of the pickup layer and thetransportation of the combined layer to the contact section and also apart of the time spent in the contact section itself. This time periodcan be compared with the prior art contact time between the possiblysurface-treated substrate and the first curable compound in therecesses, which is limited only to a part of the contact section toestablish the adhesion.

The extent of curing of the first curable compound also has an effect onthe ability to transfer the first curable compound in the recesses tothe substrate sheet, i.e. the ability to withdraw the curable compoundfrom the recesses. The extent of curing can be controlled beforeremoval, but also the curable compound remaining in the recesses afterremoval of excessive curable compound and application of the pickuplayer can be further cured prior to and/or during contact with thesubstrate sheet. In other words, in one embodiment of a manufacturingmethod, the final curing is, at least to a part, performed during thestep of transferring.

A strong bond between the pickup layer and the first curable compound inthe recesses opens up additional advantages. A high contrast in theproduced product micro features can be achieved by using the thicknessof the print, i.e. using recesses in the matrix having a large depth. Alarge depth, however, makes the release from the recess harder toperform. However, with the firm attachment between the pickup layer andthe first curable compound, also relatively thick prints can beachieved.

If a high resolution is required in the final product micro features orif complex shapes are requested, the aspect ratio of the recessestypically increases. The amount of side walls in the matrix surface,directed in very different directions, increases and thereby theseparation of the cured first curable compound from the recess becomesheavier. Also here, with the firm attachment between the pickup layerand the first curable compound, also prints emanating from high aspectratio matrixes can be achieved.

With reference to FIG. 1, a product manufactured according to the abovepresented ideas may have one or more additional product micro features3, e.g. lenses 2, provided in or on the substrate sheet 5 by embossingin the substrate sheet 5 or by applying a coating to the surface of thesubstrate sheet 5. Each additional product feature 3 being associatedwith a printed product feature 3 on the opposite side of the substratesheet 5 may thereby form a focusing element 2 and an image object 4 pairfor a synthetic image device. The product micro features 3 can beprovided in any order, i.e. in the present embodiment first the lenses2, followed by the image objects 4, or the image objects 4 followed bythe lenses 2, or all product micro features 3 at the same time.

Further additional product micro features can also be providedindependently or aligned with product micro features 3 with the sameprocesses or different processes. The substrate sheet 5 may also beprovided with product micro features pre-formed in or on the substratesheet 5.

An important aspect of the product properties is the substrate sheetthickness since this at least partly determines the alignment in thethickness direction of product micro features on opposed sides of thesubstrate sheet. In prior art solutions with low-viscous surfacetreatments on the substrate, the substrate sheet thickness cannot bemodified very much. However, by having a pickup layer on top of thecurable compound in the matrix recesses, the situation is completelydifferent.

During pre-treatment, the substrate sheet thickness can in oneembodiment be modified by the deposition of the pickup layer comprisingthe second curable material in order to form an offset layer on thesubstrate sheet. The thickness of this offset layer can be controlledand, if necessary, varied during production.

In another embodiment, more than one pick-up layers are provided on topof each other. In such embodiments, the innermost pickup layer can beoptimized for establishing a good adhesion to the curable compound inthe recesses and may e.g. have a relatively high viscosity. On top ofthis layer, an additional pickup layer may be provided, which e.g. has alower viscosity for improving the wetting properties against thesubstrate.

The pickup layer comprises a second curable material and is oftenreferred to as a lacquer. However, the pickup layer 6 may alsoadditionally comprise non-curable constituents.

The application of the pickup layer may include the deposition ofdifferent primers or solvents, etching etc. in order to modify thesurface properties of the first curable compound to obtain improvedadhesion. Surface modification can also be applied on the outer surfaceof the pickup layer in order to modify the adhesion properties relativeto the substrate. An increase in adhesion is typically accomplished byan increase of the surface energy of the pickup layer.

The pickup layer may also in addition be pre-cured to some extent priorto contact with the substrate, and/or cured after being withdrawn fromthe matrix.

In optical applications the pickup layer is preferably transparent orpartly transparent. Filling and selective removal of first curablecompound can be assisted by manipulation of the surface properties ofthe matrix, i.e. by having comparatively hydrophilic recesses andcomparatively hydrophobic intermediate surfaces between the recesses.This can be accomplished e.g. by having a Ni matrix with cavities filledwith silicone, etching recesses so as to obtain a surface texture in therecesses that provides a more hydrophilic surface than the intermediatenative surfaces, or coating of intermediate surfaces with hydrophobicpolytetrafluoroethylene or the like.

FIG. 4 illustrates schematically an embodiment of an arrangement 99 forcontinuous production of a printed product. A matrix roll 20 has acircumferential surface 24 with recesses 22. A drive unit 52 arrangedfor rotating said matrix roll 20 in a rotational direction 26. A firstapplicator 15 is arranged for application of a first curable compoundonto the matrix roll 20 so as to fill the recesses 22 with the firstcurable compound. In a particular embodiment, the first applicator 15comprises an anilox roll, whereby a well determined amount of the firstcurable compound can be applied. The first curable compound is in thisparticular embodiment then transferred to the matrix roll 20 via acliché cylinder of rubber.

The amount of the first curable compound is in one embodiment easilycontrolled by controlling a so-called K-factor, i.e. the relativevelocity ratio between the contacting parts of the anilox roll and thecliché cylinder. A lower speed of the circumferential surface of theanilox roll, i.e. a K-factor less than 1, gives a lower amount of thefirst curable compound on the cliché cylinder, which in turn means asmaller amount of the first curable compound provided to the matrix rollper time unit. Similarly, a circumferential speed of the anilox rollsurface that is higher than the speed of the cliché cylinder surfacegives a higher amount of the first curable compound on the clichécylinder. Thus, by controlling the relative rotational speed, the amountof the first curable compound provided to the matrix roll can becontrolled, e.g. to suit the pattern in the matrix roll.

A second applicator 30, separate from the first applicator 15, isarranged for covering the circumferential surface 24 and the recesses 22filled with the first curable compound by a pickup layer 6 of a secondcurable compound.

Also the relative velocities of the cliché cylinder and the matrix rollmay be controlled in the second applicator in particular embodiments.When the cliché cylinder leaves the second curable compound onto thesurface of the matrix roll, the contacting surfaces have typicallyessentially the same velocity. The second curable compound is pushedinto any remaining parts of the recesses of the matrix roll, not filledby the first curable compound. This can be the case e.g. if the patternof recesses is very complex with e.g. small features with high aspectratios, or if the matrix roll comprises non-perfect joints. In thecontact between the cliché cylinder and the matrix roll a front of thesecond curable compound is typically built up in front of the contactingpoint, which typically fills most dimplings or other similar unfilledcavities. However, despite such a build-up of excess material, volumesfollowing or preceding e.g. a joint in the tool may still not be filledcompletely, e.g. due to shadowing effects. In other words, thegeometrical form can cause the build-up of material to pass areas justbehind e.g. defects or joints without reaching into every volume.

In order to improve the filling properties, the relative speed betweenthe cliché cylinder and the matrix roll may be changed, which introducesa sliding component in the contact between surfaces of the clichécylinder and the matrix roll. If the circumferential surface of thecliché cylinder is controlled to be faster than the surface of thematrix roll, the cliché cylinder will slide relative to the surface ofthe matrix roll in a direction of the rotation direction of the matrixroll, i.e. in opposite direction to the material build-up. By thisrelative sliding, the first curable compound can be provided to parts ofthe matrix surface that otherwise are difficult to reach, e.g. due tothe above described shadowing.

A similar effect is achieved if the circumferential surface of thecliché cylinder is controlled to be slower than the surface of thematrix roll. The relative sliding direction will then be the opposite.

Thereby, depending on the actual pattern of the matrix roll and/orjoints in the matrix roll surface, the relative speed of the between thecliché cylinder and the matrix roll may be changed to achieve a betterfilling of the recesses.

Substrate guides 46, 48 are arranged for bringing a substrate sheet 5 incontact with the matrix roll 20 in a contact section 35. The contactsection 35 is situated, in the rotational direction 26, after the secondapplicator 30. The pickup layer 6 and the first curable compound aretransferred together from the circumferential surface 22 and left on asurface 10 of the substrate sheet 5. Thereby the first curable compoundforms printed product micro features 3 at the pickup layer 6 coveringthe substrate surface 10. The arrangement 99 further comprises curingmeans 50. The curing means 50 is arranged for curing the first curablecompound and the second curable compound. The curing means 50 isarranged to perform the curing at least to a part within the contactsection 35. A final curing can also be performed after the contactsection 35 is left.

The first applicator 15, the second applicator 30 and the substrateguides 46, 48 are arranged around the matrix roll 20. The firstapplicator 15 and the second applicator 30 are illustrated as rolls,however, as discussed further above, they are not limited to this. Thesubstrate sheet 5 is in the embodiment of FIG. 4 guided by a pressureroll 46 and a peeling roll 48. In the zone between these rolls, thesubstrate sheet 5 follows the surface of the matrix roll 20. In otherwords, the contact section 35 is in the present embodiment defined bythe positions of the pressure roll 46 and the peeling roll 48. Asappreciated by a person skilled in the art, the precise placement of thedifferent components is not limited to exactly the set-up shown in FIG.3, but can in alternative embodiments be altered.

In other words, the matrix that is designed as the mould for the productmicro features is thus preferably provided on a roll and at least thetransferring of the first curable compound and the pickup layer isperformed in a roll-to-roll process wherein at least the printed productmicro features are continuously formed on the substrate sheet that isbrought into rolling contact with the matrix roll.

In operation, the substrate sheet 5 is provided and fed between thepressure roll 46 and the matrix roll 20 and then between the peelingroll 48 and the matrix roll 20, whereby the substrate sheet 5 is broughtinto rolling contact with the matrix roll 20 around a section of thematrix roll 20. As being described above, at a first position around thematrix roll 20 a first curable compound is applied to the matrix roll 20whereby the recesses 22 in the circumferential surface 24 of the matrixroll 20 are at least partly filled with the first curable compound.Preferably the viscosity of the first curable compound is adapted toenable it to fill the smallest recesses. In one preferred embodiment ofan arrangement 99 for continuous production of a printed product,excessive first curable compound outside the recesses 22 is removed byremoval means 40 arranged at a second position around the matrix roll20. Since the removal means 40 is not absolutely compulsory, it isillustrated by broken lines. The removal means 40 is thus arranged forremoval of excessive the first curable compound from the circumferentialsurface 24 of said matrix roll 20 outside the recesses 22. The removalmeans is arranged, with respect to the rotational direction 26, beforethe second applicator 30.

The removal means 40 may in different particular embodiments comprise asqueegee and/or a polishing means. One example of a polishing means is afibre cloth arranged on a roll that is arranged to contact the matrixroll surface. Two or more removal means 40 can in certain embodiments bearranged in sequence to efficiently remove excessive first curablecompound, e.g. a squeegee followed by a polishing means. Thereby theamount of excessive first curable compound left on intermediate surfacescan be minimised, which improves the polishing.

In one preferred embodiment of an arrangement 99 for continuousproduction of a printed product, pre-curing means 42 for increasing theviscosity of the first curable compound before removal of excessivefirst curable compound is arranged at least in-between the applicator 15and the removal means 40. Since the pre-curing means 42 is notabsolutely compulsory, it is illustrated by broken lines. Thus, thepre-curing means 42 is arranged for pre-curing the first curablecompound in the recesses. The pre-curing means 42 is arranged to performthe pre-curing at least to a part before the removing of excessive firstcurable compound. The pre-curing means 42 is arranged, with respect tothe rotational direction 26, before the second applicator 30.

Optionally, removal means may arranged at a position between theapplicator 15 and the pre-curing means 42 to permit a coarse removal ofexcessive first curable compound. Thereby the viscosity of the firstcurable compound can first be optimised for filling of the first curablecompound into the recesses 22 and then optimised by at least beingpartly cured to permit efficient removal of excessive first curablecompound without removing the first curable compound from within therecesses 22. The first curable compound is at this step not necessarilyfully cured, indeed it does not have to be cured at all when viscosityis increased by other means. Additional curing may be performed atsubsequent steps. Depending on the mechanism used for increasing theviscosity different curing means, such as a lamp (UV, infrared, etc.), aheat source, a cooling means or an electron beam gun, may be used. Inone embodiment of the invention pre-curing means 44 may in addition bearranged in sequence with the applicator 30 at a position prior to wherethe matrix roll 20 is brought into rolling contact with the substratesheet 5. At this position both the first and second curable compound canbe cured, or further cured, if it has been partly cured before, but notnecessarily fully cured.

Moreover, additional rolls, removal means and curing means may bearranged around the matrix roll and/or at the substrate sheet in orderto accomplish the embodiments of the method as described above, forexample additional applicators and removal means would need to bearranged at the matrix roll to accomplished the iteration of the stepsof applying and removing.

At a third position, at the beginning of the contact section 35, thesubstrate sheet 5 is brought into contact with the pickup layer 6 on thematrix roll 20 covering the first curable compound in the recesses 22 bymeans of the pressure roll 46. The pickup layer 6 adheres to thesubstrate sheet 5. When the substrate sheet 5 is released from thecircumferential surface 24 of the matrix roll 20 at the peeling roll 48the first curable compound in the recesses 22 is peeled out from therecesses 22 and thereby transferred to the substrate sheet 5 to form theproduct micro features 3 on the pickup layer in turn on top of thesubstrate sheet 5.

Curing means 50 is in one embodiment arranged at a position where thematrix roll 20 is in rolling contact with the substrate sheet 5. It canbe used for additional curing, or, if no curing has been madepreviously, a first curing, of the first curable compound in therecesses 22 and the second curable compound in the pickup layer 6 beforetransfer of the first curable compound from the recesses 22 to thesubstrate sheet 5. In other words, the curing means 50 is arranged toperform the curing at least to a part in the contact section 35.

In a further embodiment of an arrangement 99 for continuous productionof a printed product, illustrated in FIG. 5, means 99″ for providingadditional product micro features, such as e.g. lenses 2, on thesubstrate sheet 5 on one side of the substrate sheet or both areprovided. In this particular embodiment, the means 99″ for providingadditional product micro features comprises another set of printingequipment analogue to the previous described one, where recessescorresponding to lenses 2 are provided in a matrix roll 20″. A firstapplicator 15″ provides a first curable compound into the recesses. Asecond applicator 30″ provides a pickup layer on top of the lenses tobe. A substrate sheet 5 is provided from a supply roll 60 and the lensesare printed onto the substrate surface 10. The means 99″ for providingadditional product micro features thus forms additional product microfeatures, e.g. in the form of micro lenses 2 on one side of thesubstrate sheet 5. After provision of the other printed product microfeatures 3, e.g. image objects 4 on the other side of the substrate 5,the printed product is collected at a collection roll 66.

An advantage by using a pickup layer also at the provision of thespherical micro lenses 2 is that it reduces the risk of encapsulatingair volumes into the product, as is the case if the first curablecompound is contacted directly to the substrate surface or on asubstrate surface provided with a covering wetting layer.

In alternative embodiment, the means for providing additional productmicro features may comprise means based on different techniques andprocess types such as, different types of printing, embossing,continuous casting, surface coating, laminating, or combinationsthereof. Examples of printing techniques comprise screen printing,offset printing, flexographic printing, ink-jet printing and of courseprinting in accordance with the method of the present invention.

In a preferred embodiment, the substrate sheet is at least in the areasthat contribute to generation of a synthetic integral image transparentor translucent. Other areas may be opaque or have reduced transparency.For some optical applications the transparency may be of uttermostimportance, however, for other applications, reflecting layers areinstead required. The substrate sheet may thus in different applicationscomprise paper, films or metal, such as aluminium. Although the aboveillustrated embodiments are primarily illustrated with a substrate sheetconstituted by a single layer, it is not limited to this. In alternativeembodiments, two or more layers can be joined by techniques known in theart. The substrate sheet may in different embodiments be cast,calendared, blown, extruded and/or biaxially extruded. The substratesheet may comprise polymeric compounds such as any one or more selectedfrom the group comprising polythyleneterephthalate,polymetylenemetacrylate, polypropylene propafilm, polyvinylchloride,rigid pvc, cellulose, tri-acetate, acetate polystyrene, polyethylene,nylon, acrylic and polytherimide board. Papers made from wood pulp orcotton or synthetic wood free fibres or the like can also be used. Thepaper may be coated, calendared or machine glazed.

The matrix or matrix roll, may in one embodiment involve a printingplate. Such a printing plate is preferable fabricated using microfabrication methods such as photolithographic techniques or e-beamdirect writing, which are well known in the field of microsystemstechnology and microelectronics. This enables very high resolution, i.e.better than 0.5 μm. In other words, the used line width can in specificembodiments be at least down to 0.5 μm, due to the improved adhesionproperties. Typical depths of the recesses can be in the order of 1-2μm, giving aspect ratios of 2-4. Resolution, depth of the recesses andaspect ratio is preferably designed from case to case. The masterstructure is a negative copy of the printing plate and can be used tomanufacture numerous printing plates. The pattern of the masterstructure can be transferred to the matrix by replication. Nickel (Ni)is a suitable material for replicated printing plates and plates made ofthis material are plated on the master. A printing plate manufacturedwith micro fabrication methods generally does not have the rigidityrequired for the means for providing product micro features according tothe invention. Thus the printing plate is preferably attached to acarrier that provides the necessary rigidity. In the above describedroll-to-roll process the printing plate can be attached to the surfaceof a roll to form the matrix roll.

In a typical matrix roll, one, two or more printing plates are attachedtogether. Typically, the edges are welded, which gives rise tonon-usable areas at the matrix roll. However, if the geometricaldimensions of such joints are kept small, the total effect can belimited. In particular embodiments, seamless tools can also be used,where the printing plate is produced directly in a cylindrical shape.

The wear resistance of the matrix roll can be improved by surfacetreatment, such as hardening and/or deposition of thin wear resistantcoatings, for example TiN. Other alternatives of a wear resistantcoating can be e.g. diamond-like carbon or chrome nitride. A typicalthickness of such a wear resistant coating is 100-120 nm. However,thicknesses in the range 50-300 nm or even 50-500 nm are perfectlyuseable. The maximum thickness is typically limited by the requestedresolution. A thick wear resistant coating adds on material also on thevertical sides of a recess, which modifies the recess pattern. Thickwear resistant coatings also tend to create protruding volumes, inparticular in connection with sharp edges, which may make the releasingfrom the recesses of first curable compound more difficult. The minimumthickness of the wear resistant coating is often set by productioneconomy reasons, since even a covered surface will experience a certaindegree of wear.

The wear of the tool depends also to a high degree on the properties ofthe first curable compound. Corresponding wear resistant coatings couldbe lasting several times longer for one ink compared to another. Forinstance, white ink with abrasive TiO₂ as a first curable compound wasfound to cause a high wear.

When the wear resistant coating is worn out, it is possible to perform areconditioning of the tools. First remaining wear resistant coating isetched away. For TiN coatings, etching liquids such as RCA1 can be used,comprising NH₄OH, H₂O₂ and H₂O. A ratio of 1:2:5 of these componentsoperates well at a temperature of 60° C. However, also othercompositions and temperatures will be operable. The Ni surface operatesas an efficient etching stop for these liquids, which makes it easy tocontinue the etching until the surface is free from old coatings.Thereafter a new wear resistant coating can be deposited.

Alternatively or as a complement, nitrogen can be added during the Niplating step, thereby creating wear resistant nitride materials. Thehardness of the Ni surface can be thus be improved. Also otheradditives, such as phosphorus can be used in this manner to improve theNi surface hardness by nickel phosphides.

The improvement of the Ni surface can in particular embodiments also becombined with an additional wear resistant coating.

Also in the embodiment of FIG. 5, there is a wetting layer applicator62, positioned before the second matrix roll 20. This applicator 62 isarranged for providing a thin wetting layer 68 on the substrate 5,thereby modifying the substrate surface 10 before it is contacted withthe pickup layer 6. This arrangement has the advantage that it ispossible to even further adapt, typically enhance, the adhesionproperties between the pickup layer 6 and the substrate 5. By having twosubstantially continuous layers with appropriate properties on the twosurfaces that meet at the entrance to the contact section, the contactpressure can be reduced and the risk for artefacts in the final productcan be further reduced. As being obvious from the name, the wettinglayer improves the wetting between the pickup layer and the substrate.However, an additional advantage is that the wetting layer also reducesthe turbulence of material at the entrance of the contact section. Thewetting layer is typically also a curable compound, which eventually iscured together with the second curable compound of the pickup layer andthe first curable compound of the printed product micro features to be.The curable compound of the wetting layer may be the same as the firstcurable compound or the second curable compound or it may be anothercurable compound. In other words, the manufacturing method comprises thefurther step of providing the substrate with a wetting surface layerbefore bringing the matrix in contact with the substrate surface.

In embodiments, where the pickup layer is combined with a wetting layeron the substrate, or where there are two pickup layers on top of eachother, the two continuous layers can be used in different combinationsfor achieving particular advantages. The materials in the two layers canbe selected to have different properties, e.g. different opticalproperties, different viscosity, different adhesion properties,different curing properties etc. In one, non-limiting, example, thepickup layer closest to the actual features can have differentrefractory index than the surrounding materials. The layer closest tothe substrate may then instead be optimized for improving adhesionproperties. In another, also non-limiting, example, the pickup layerclosest to the actual features can have a relatively high viscosityenabling compensation of variations in e.g. the substrate thickness. Inthis example, this layer comprises a material having a relatively highdegree of polymer. In the layer closest to the substrate, adhesionproperties are of more interest and another compound comprising a higherdegree of monomers are therefore selected. As anyone skilled in the artunderstands, this can be varied in numerous ways depending on theintended applications of the final printed product.

This provision of a wetting layer is not exclusively usable with theembodiment of FIG. 5, but can be combined with any other embodiments.Likewise, the main embodiment of FIG. 5 may be performed without theprovision of a wetting layer.

In particular embodiments, more than one arrangement 99 for continuousproduction of a printed product can also be provided on one and the sameside of the substrate. Such an arrangement can thereby be used e.g. toprint product micro features of different colours. It could also beuseful when printing product micro features of so differing shapes orsizes that the use of two different matrixes is favourable. Suchmultiple printing units can be combined with any of the previous shownembodiments, for example, but not limited to the embodiments shown inFIGS. 4 and 5.

In one embodiment of the present invention supporting structures areprovided in the recesses of the matrix in order to improve filling oflarge recesses by use of capillary forces.

FIG. 6 schematically illustrates two recesses 72 a, 72 b being filledwith a curable compound 73. Supporting structures 71, such as pillars orridges, are provided in the recesses 72A, 72 b. Liquid curable compoundfills both a small recess 72 a and a larger recess 72 b. The width ofthe supporting structures 71 is preferably adapted to be so small thatany artefacts in the geometry of the printed product micro featurescaused by them will not be perceived by an observer when the product isin normal use. The height of the supporting structures 71 typicallyequal to the depth of the recesses due to fabrication issues, however,is not limited to this. The distance between the supporting structuresis adapted so that capillary forces can act on the curable compoundfilled into the recesses to enable complete filling of the recesses.Preferably, when the printed product micro features are used in opticaldevices the supporting structures are distributed in a disordered mannerto reduce artefacts as if the supporting structures are arranged in anordered array, small artefacts of the printed product micro featuresoriginating from the supporting structures may be perceived in normaluse. The supporting structures are preferably positioned randomly or atleast varied in such a way that they will not give rise to any moiréeffect.

This approach can advantageously be utilized when a pattern of printedproduct micro features is to be provided, which is dominated by “filled”surfaces, i.e. the matrix comprises mainly “open” surfaces. This isparticularly true in embodiments where the parts of the matrix thatprotrudes between the open areas have small line width, in a preferredembodiment typically below 5 μm. However, in other embodiments, the linewidth may also be larger than that. If a controlled amount of ink isapplied, which does not exceed the volume of the open areas, the surfacechemical and physical properties can be adapted so that the ink byitself is collected in the open areas. The ink can thereby beself-orienting so as to creep down in the recessed areas, leaving theprotruding surfaces substantially free from ink. Typically then, thereis no need for any removal of excess ink or polishing. The process canthen continue as earlier described, e.g. by pre-curing, covering with apickup layer and a final curing when applied at a substrate.

In some embodiments, this self-orienting of the ink is facilitated ifthe line width of the protruding parts is small and if the viscosity ofthe ink is low. As a non-limiting example, if the depth of thestructures is 2 μm, a zone of 2-3 μm from the edge will act to draw theink down in the structure instead of letting it stay on the top surface.This means that if there is a pattern of lines with a line width of 4-6μm, the ink, at a properly provided amount, will creep down in therecesses between these protrusions.

On the other hand, the distance between the protruding parts cannot betoo large, since the capillary forces attracting the ink towards theedges of the structures than may be too weak. In a tested example wherea depth of the structure was 2 μm, a preferred embodiment has a distancebetween the structures that is typically not larger than typically 10μm. If the distance in that example becomes much larger than that, theink tends to stick to the edges, leaving the central part of the recessempty or at least partially empty from ink. A recessed surface of 20 μmtherefore suffers from a lack of ink in the middle. If the recessedsurface is further increased, the depleted zone comes at an approximatedistance of 10-15 μm from the walls, whereas the central part of therecess has remaining ink. However, in other embodiments, where the inkproperties, matrix surface properties and depths are different, themaximum distance may also be different. The use randomly positionedsupport structures may also mitigate such effects.

In order to obtain the above mentioned self-orienting of the ink putshigher demands on the design of the pattern. The patterns are preferablyadapted to the differences in surface properties between ink and matrix.The capillary forces in the negative corners of the structures shouldtypically exceed the surface tension that acts for keeping the ink atthe surfaces of the protruding parts. In practice, the pattern cannot beallowed to involve too large flat protruding surfaces.

Another aspect influencing this self-orienting of the ink is that thesurfaces that should capture the ink should preferably not be closed.This means that if e.g. a ring structure is provided with a line widthof 4 μm, with a circular hole inside, it may be difficult to fill thehole if it is too small. The ink may be prohibited from entering thehole due to gas bubbles forming, or the hole may be overfilled wherebyink stays on the protrusion surfaces. A preferred way is then to use anopen recess pattern over the entire matrix surface. In such a way, anink wave can be driven within the tool upon contact with the applicator.

This approach with self-orienting ink, removing the need for an excessink removal step is particularly useful at high speed manufacturing.

The method and the arrangement of the present teachings enable printingof printed product micro features on substrate sheets with high accuracyin printing with respect to lateral resolution, edge definition anddimensional tolerances in three dimensions that is not achievable withconventional printing techniques. Moreover, the method and arrangementallows for continuous processing, which enables this accuracy to beobtained on large surfaces. In particular products comprising printedproduct micro features ranging in lateral size from 0.5 μm×0.5 μm tocentimetre sized features having a height of 0.5 μm to 5 μm, preferably1 to 3 μm, hence yielding an aspect ratio varying from 4:1(height:width) to 1:10000, can be formed. The features can for examplebe as small as 0.5 μm×0.5 μm×2 μm or 1 μm×1 μm×1 μm. As mentioned above,when lateral dimensions vary this much and the product includes μm-sizedfeatures, i.e. recesses, the filling of the curable compound ischallenging. In order to fill the small recesses the viscosity needs tobe comparatively low. This imposes a problem for large recesses sincethe capillary forces cannot help in filling these large structures.Instead surface tension may play a significant role.

With the use of the pickup layer provided at the matrix roll, theprinting speed can be allowed to be high. Favourable tests have beenmade at different speed with essentially no difference in patternquality. These test runs are performed without particularly adapting allparameters. By a proper selection of ink properties, pre-curing levelsand pattern design, printing speeds of 100-150 cm/s are considered asperfectly feasible.

The present disclose presents solutions for enabling high speedmanufacturing of printed products. One contributing aspect is anincreased adhesion between the print and the substrate. This in turnimproves the possibilities to provide increased resolution and bettercontrast.

All references to height, width, thickness direction, lateral etc. areintroduced for the easy of understanding only, and should not beconsidered as limiting as specific embodiments. Further, the dimensionsof the structures in the drawings are not necessarily to scale. Forexample the size of the product micro features and layer thicknesses aretypically strongly exaggerated.

The embodiments described above are to be understood as a fewillustrative examples of the present invention. It will be understood bythose skilled in the art that various modifications, combinations andchanges may be made to the embodiments without departing from the scopeof the present invention. In particular, different part solutions in thedifferent embodiments can be combined in other configurations, wheretechnically possible. The scope of the present invention is, however,defined by the appended claims.

The invention claimed is:
 1. A method for manufacturing a printedproduct, comprising the steps of: a) providing a matrix comprising amatrix surface having at least one recess; b) applying a first curablecompound to said matrix surface and said at least one recess in acontrolled amount that does not exceed a volume of said at least onerecess; wherein said first curable compound creep down in and partlyfill said at least one recess, leaving protruding surfaces substantiallyfree from said first curable compound; c) covering said matrix surfaceand said at least one recess partially filled with said first curablecompound by a pickup layer of a second curable compound; d) bringingsaid matrix in contact with said substrate surface; e) curing, at leastpartly, said first curable compound and said second curable compound;and f) separating said matrix surface from said substrate surface,leaving said first curable compound on said substrate surface; whereinsaid pickup layer and said first curable compound filling said at leastone recess are transferred together from said matrix surface onto asubstrate surface of a substrate sheet; wherein said first curablecompound forms printed product micro features at said pickup layercovering said substrate surface.
 2. The method according to claim 1,wherein said applying comprises forming of a depleted zone in a centralpart of said at least one recess.
 3. The method according to claim 1,wherein said at least one recess constitutes an open recess pattern. 4.The method according to claim 1, further comprising the step of:pre-curing said first curable compound in said at least one recessbefore said step of covering said matrix surface and said at least onerecess filled with said first curable compound by a pickup layer.
 5. Themethod according to claim 1, wherein said first curable compound isdifferent from said second curable compound.
 6. The method according toclaim 5, wherein said second curable compound has a different refractoryindex than said first curable compound.
 7. The method according to claim1, comprising the further step of: providing said substrate with awetting surface layer before said step of bringing said matrix incontact with said substrate surface.
 8. The method according to claim 1,comprising the further step of: providing said substrate with a wettingsurface layer before said step of bringing said matrix in contact withsaid substrate surface.
 9. An arrangement for continuous production of aprinted product, comprising: a matrix roll having a circumferentialsurface with at least one recess; a first applicator arranged forapplication of a first curable compound onto said matrix roll in acontrolled amount that does not exceed a volume of said at least onerecess; wherein said first curable compound creep down in and partlyfill said at least one recess, leaving protruding surfaces substantiallyfree from said first curable compound; drive unit arranged for rotatingsaid matrix roll in a rotational direction; a second applicator,separate from said first applicator, arranged for covering saidcircumferential surface and said at least one recess filled with saidfirst curable compound by a pickup layer of a second curable compound;substrate guides, arranged for bringing a substrate sheet in contactwith said matrix roll in a contact section; wherein said contact sectionis situated, in said rotational direction, after said second applicator;and curing means; wherein said pickup layer and said first curablecompound are transferred together from said circumferential surface andleft on a substrate surface of said substrate sheet; wherein said firstcurable compound forms printed product micro features at said pickuplayer covering said substrate surface; and said curing means beingarranged for curing said first curable compound and said second curablecompound; said curing means being arranged to perform said curing atleast to a part in said contact section.
 10. The arrangement accordingto claim 9, further comprising a pre-curing means, arranged forpre-curing said first curable compound in said at least one recess, saidpre-curing means being arranged, in said rotational direction, beforesaid second applicator.
 11. The arrangement according to claim 9,further comprising a wetting layer applicator arranged for providing awetting layer on said substrate.
 12. A synthetic image device,comprising: a transparent substrate sheet; an array of focusingelements, arranged at a first side of said transparent substrate sheet;an array of image objects, associated with said focusing elements andarranged at a second side of said transparent substrate sheet, oppositeto said first side; and a pickup layer provided between said array ofimage objects and said transparent substrate sheet; said image objectsbeing printed product micro features formed by bringing a matrix incontact with a surface of said transparent substrate sheet, said matrixhaving at least one recess partly filled with a first curable compoundand protruding surfaces substantially free from said first curablecompound, and curing said first curable compound.
 13. The syntheticimage device according to claim 12, wherein said pickup layer has adifferent refractory index than cured said first curable compound. 14.The synthetic image device according to claim 12, wherein said imageobjects present said first curable compound attracted to edges of saidimage objects.
 15. The synthetic image device according to claim 12,wherein said image objects present depleted zones, empty or at leastpartially empty from said first curable compound, in a middle of saidimage objects.
 16. The synthetic image device according to claim 12,wherein said image objects present said first curable compound attractedto edges of said image objects.
 17. The synthetic image device accordingto claim 12, wherein said image objects present depleted zones, empty orat least partially empty from said first curable compound, in a middleof said image objects.
 18. The method according to claim 2, wherein saidat least one recess constitutes an open recess pattern.
 19. The methodaccording to claim 2, further comprising the step of: pre-curing saidfirst curable compound in said at least one recess before said step ofcovering said matrix surface and said at least one recess filled withsaid first curable compound by a pickup layer.
 20. The method accordingto claim 19, further comprising the step of: pre-curing said firstcurable compound in said at least one recess before said step ofcovering said matrix surface and said at least one recess filled withsaid first curable compound by a pickup layer.